dc.description.transcription | [Four Corners] Reprinted from the Proceedings of the NATIONAL, ACADEMY OF SCIENCES, Vol, 10, No. 7. July, 1924 ON ASTONY METEORITE FROM (ANTHONY HARPER COUNTY, KANSAS AND A RECENTLY FOUND METEORIC IRON FROM MEJILLONES, CHILE BY GEORGE P. MERRILL UNITED STATRS NatIoNaL MUSEUM Communicated May 8, 1924 In the course of my work on the Minor Constituents of Meteorites, the results of which have been given in the PrOcEeDINGs and MEMOIRS of the Academy, several undescribed individuals from falls of unknown date have come to hand, two of which are described below: _ On a Stony Meteorite from Anthony, Harper County, Kansas.*_ The stone described below was first shown the writer when visiting the State Agricultural College at Manhattan, Kansas, in November 1923, by Professor Arthur B. Sperry. To it was attached a written label reading: Nickel-Iron meteor, found on Sec. 31, Tunshp. 23, R. 5, west 6 P. M. (6½ miles east and 1 mile south of Anthony, Harper County, Kansas) Aug. 1919 by S. T. Elliott in ploughing. The stone was considerably oxidized and one or two prominent points were broken away, but the pittings were very evident (see PI. 1) and its meteoric nature unmistakable. 'Through an arrangement with Professor Sperry the stone has been cut in halves a cast being first made and portions submitted to analysis. The general appearance of the stone before cutting is shown in the two views of the plate. The dimensions were 33 em. X 24 em. X 16.5 cm. and the weight 19.5 kilograms. A rough estimate of the amount broken away would place the original weight of the mass at 20 kilograms. The shape is such as to suggest that it is but a fragment from a larger mass of which the face shown in figure 2 was the ruptured surface. The stone was cut through the center in the hope a vain one as it proved--that the interior might have escaped oxidation and afford satisfactory material for sections and analyses. [Plate 1 The Anthony, Kansas Meteoric stone in reversed position.] Unfortunately these hopes were only partially realized, the oxidation staining the stone in spots throughout, though naturally somewhat unequally The cut surface of the stone is of a dark gray-brown color mottled with darker brown from the secondary iron oxide. The structure, notwithstanding the oxidation which stains all portions alike, is plainly chondritic to the unaided eye. The metallic constituent occurs in minute disseminated granules, in spongy-form aggregates sometimes enclosing sulphide nodules, and in slender, more or less disconnected string-like forms 20 to 30 mm in length. The microscopic examination, in thin sections, was somewhat disappointing, owing to the iron staining. The mineral composition is very simple, consisting, aside from the metal and sulphide, only of olivine and a rhombic pyroxene. If other minerals are present they are obscured by oxidation. The chondrules are of the ordinary stereotyped form and need no special description. Porphyritic and barred types of olivine forms are common, as are also the radiate and cryptocrystalline forms of enstatite. No feldspars nor monoclinic pyroxenes were observable. Small quantities of lawrencite made their presence known in the form of exuded drops on a freshly cut surface. Fragments immersed for but a few minutes in dilute nitric acid gave a solution reacting for phosphorus and lime, indicating the presence of the usual interstitial phosphate, now obscured by oxidation. A chemical analysis by Doctor J. E. Whitfield yielded: Metallic constituent 20.90% Silicate constituent 79.10% As will be noted the stone is low in silica and magnesia and above the average in content of metal, as shown in my list of selected analyses.2Otherwise it presents no features unusual to stones of its class. Doubtless had it been sought a considerable amount of water would have been yielded by the secondary oxide. The discoloration by this oxidation renders it difficult to classify exactly, but I am disposed to place it in the group of gray chondrites. [PLATE 2 The Mejillones iron in reversed positions.] A Recently Found Meteoric Iron from Mejillones, Chile.**_ The meteoric iron described below (see PI. 2) was obtained through Ward's Natural Science Establishment. No records accompanied it other than that given on an attached adhesive slip on which was the following inscription: Meteorite Sissidere. Caido entre el grado 23° y° 24° Mayo 1905. Region Mejillones. 31 libras. This was somewhat puzzling, since there is no record of a fall at this date. The Mejillones iron of which we have record was found prior to 1874 and was described by Domeyko in 1875. On request the firm mentioned therefore wrote their Chilean correspondent and obtained the following additional and confirmatory matter: "Aerolithe Sissidere, from Mejillones: Was found by the miners Jose Rivera and Manuel Ascencio Rocha in the region between the Morro (Hill) de los Guaneros de Mejillones and Caleta Herradura Grande (Big Horseshoe Harbour, literally), between latitude 23 and 24, nearer to 24. The distance from the sea is about 9 kilometers and the falling spot is a nameless sandy "pampa." Was bought from the finders in 1905." This does not entirely clear up the matter since the mass received at the Museum is a practically complete individual, only a corner and sharp edge that could not have yielded more than 200 grams of material at most, having been broken away. As received it was some 12 X 14 X 28 cm. in dimensions and weighed 14,580 grams, perhaps 14,700 before the portions mentioned were broken off, while the original Mejillones is reported of such size that a cart would be requisite for its carriage to post. An etched surface shows a finely, even granular surface (see PI. 3) but without trace of Neumann lines, nor are the little areas of schreibersite arranged in any discernible definite order. The granulation is apparently of the same nature as that in the Forsyth County iron, but is somewhat coarser, many of the granules, measured on the polished surface, being a millimeter or more in diameter. The dark area shown in the figure has a center of schreibersite granules surrounded by troilite and this in turn by a wider border of finely granular metal. The appearance is suggestive of the segregation nodules sometimes found in terrestrial rocks. An analysis by Dr. J. E. Whitfield yielded as in column I below. For purposes of comparison Domeyko's analysis® is given in column II The original Mejillones of Domeyko is classed by Brezina, Wulfing and others as a brecciated hexahedrite (Hb). I am disposed to regard the iron here described as an ataxite of the Nedagolla group (Dn). It should be noted that while differing slightly in crystalline structure, in chemical composition it is practically identical with the iron of Alpine, Texas, described by me some two years ago' the analysis of which is reproduced in column III above. [PLATE 3 Microstructure of Mejillones iron X eight diameters.] This finding seems to offer no relief from the usual confusion presented by Chilean findings. While the iron is not quite identical with the original Meiillones as described, it is sufficiently near it to suggest its identity. It is, however, very little oxidized, nor is the surface at all sandblasted as is so frequently the case with desert irons. It seems impossible that it should have lain in the ground since 1874, the date of the original Mejillones. The label states plainly fell ("caido") in 1905. On the supposition that this is an error, is it possible that this mass is the original Mejillones described by Domeyko, from which was broken the 167 grams, now in the Paris Museum and that the large mass described was Vaca Muerta? Farrington5 has called attention to the fact that nearly if not quite all of the so-called Mejillones iron in the various museums is really Vaca Muerta ON A METEORIC IRON FROM FOUR CORNERS, SAN JUAN COUNTY. NEW MEXICO BY GEORGE: P. MERRILL UNITED STATES NATIONAL MUSEUM Communicated May 16, 1924 The attention of the writer was first brought to this interesting meteorite by a letter from the late R. C. Hills, the well known mining geologist of Denver, Colorado. In this he says: "I have a meteorite weighing about fifty-five pounds* * *. It is almost a pallasite, but not quite. I have named it Four Corners, because there is no town near the location of the find, which is said to be 15 miles southeast from the common corner of Colorado, New Mexico, Arizona and Utah. I have suggested to the Trustees of the Museum (i.e., the Colorado Museum of Natural History, in Denver | that it be sent to you to cut up, analyze and describe," etc. This proposition on the part of Mr. Hills has now been carried out with the results given below. The meteorite as received has much the form of a water-worn boulder (see Plate 1) without deep pittings, two of the surfaces being rough as though broken during flight. The smooth "nose was deeply incised, as with a steel chisel. The dimensions were approximately 16.5 X 26.5 X 26.5 em. and weight 25 kilograms; that given by Mr. Hills (55 Ibs.) was shown by reweighing to be correct. The name Four Corners will be retained, as sufficiently distinctive, there being no other instance of its kind within the present limits of the United States. [PLATE 1 The Four Corners meteorite in reversed positions.] [PLATE 2 Polished slice of Four Corners meteorite. About four-fifths natural size.] [Fig. 2. Slightly magnified etched slice of the same. The black areas are the silicate areas; the light gray, kamacite and plessite; the white, taenite. Photomicrograph by Lewis E. Jewell.] [Fig. 1. Chondroidal aggregate of pyroxenes in silicate portion of the Four Corners meteorite.] The direction given, i.e., 15 miles southeast, will however throw it into the extreme northwestern part of San Juan County, New Mexico. The structure as shown in Plate 2 is quite different from that of any meteorite which I have personally examined. The metal it will be observed predominates, but is filled with dark irregular large and small enclosures up to 15 mm. in diameter which on examination prove to be very fine grained crystalline granular aggregates of pyroxenes with a little olivine, often considerable amounts of iron phosphide and sulphide, and a few feldspathic granules and particles of calcium phosphate. These enclosures are distributed throughout the mass in form of mere sand grains or angular masses up to the dimensions given. In thin section under the microscope they show occasional clustered aggregates suggestive of chondrules, one of which is shown in Figure 1, Plate 3. The pyroxenic constituents are nearly colorless enstatite and bright green diopside. It is to be noted that these enclosures are always angular and plainly fragmental. The metal itself etched with either bromine or nitric acid quickly turns dark gray but shows no other signs of oxidation. It is noteworthy that each metallic area, varying from 10 to 20 mm. in diameter shows its own crystallographic orientation as indicated by the Widmanstätten figures. This feature will again be referred to. (See fig. 2, Plate 3.) Bands of wickel-kamacite so characteristic of pallasites are here wholly lacking. The plessite areas are usually small, the taenite distinct, though having little relief on the etched surface. Schreibersite in small granular aggregates usually associated with the silicate enclosures is not uncommon Troilite in small particles associated with and distributed throughout the silicates is abundant, but there are none of the rounded nodular forms so common in meteoric irons. Small particles of metal, it should be stated, occur irregularly throughout the silicate fragments. A characteristic sample of the meteorite, (one in which the silicate portions were so distributed as to be representative of the meteorite as a whole) was submitted to Dr. J. E. Whitfield with the following results: METALLIC PORTION This, it will be observed, agrees well with the analyses of the fine octahedrite of Perryville, Missouri or the metal from the Krasnojarsk pallasite as given by Whitfield.? The silicate portion yielded 47.16% soluble in dilute hydrochloric acid and 52.84% insoluble. The soluble portion contained the olivine, doubtless a portion of the feldspar, the calcium phosphate and the iron sulphide. An accident prevented its complete analysis. The insoluble portion, a mixture of the two pyroxenes and feldspar, yielded as follows: The specific gravity of a 425-gram slice selected as typical of the mass was 6.62. Of a small piece of the metal, free from silicate enclosures, 7.88. The whole aspect of this meteorite is unusual and difficult to explain. It is obvious that the silicates could not have crystallized out of a highly ferriferous magma in their present form. Their ragged and angular shapes are wholly against this, nor can they be considered merely as fragments caught up in a molten metallic magma, as has been suggested, since they show no evidences whatever of corrosion. 'They might perhaps be accounted for by assuming them to be products of disintegration from a previously existing finely granular siliceous stone, the particles from which became admixed with some ferriferous compound reducible at temperatures considerably below the normal melting point of iron, as long ago suggested by Meunier. The fact that the individual plates of the iron, as previousiy noted and as brought out by etching are of limited extent instead of being continuous over considerable areas, as in ordinary octahedral iron, suggests however a one time coarsely granular mass of metallic and silicate fragments, since compressed. Just how much reliance can be placed upon such a suggestion is perhaps doubtful, since any crystalline aggregate, as of calcite or feldspar will show a like diversity in crystallographic orientation. The closest analogue of this iron would appear to be that of Copiapo (Dheesa) Chile described by Haidinger,3 Daubree4 and Meunier5 but of which unfortunately our Museum has no sample for comparison. An analysis of the metallic portion of the Copiapo fall by Dr. E. Dittler, as given by Berwerth® yielded: Fe 87.40, Ni 11.97, Co 0.56, schreibersite 0.07. The silicate analysis given by Meunier points unmistakably to olivine and pyroxene as the chief constituents. 'The similarity of the two is also shown by Meunier's Figure 39 in the work cited.7 The Four Corners meteorite cannot be made to conform readily with any existing and generally accepted scheme of classification. Mr. Hills described it as "almost a pallasite," but it is not like any known member of this group. From its nearest approximate, the pallasites of the Rokicky group, it differs in that in the latter the siliceous portion consists wholly of large olivine blebs in a more or less fragmental condition, while in the Four Corners the inclusions are rock fragments of a complex nature. The meteorite is really a breccia composed of fragments of a fine grained, pyroxenie rock with an excess of cementing material in the form of coarse granular nickel-iron. In this respect it differs from the Kodai Kanal iron described by Berwerth, in which the silicate fragments are crystalline secretions from a ferriferous magma. Viewed in this light it would then seem best to class it with the Copiapo (Dheesa) fall as a granular octahedral iron with silicate enclosures. 1 Proc. U. S. Nat. Museum, 43, 1912, pp. 595-597. 2 Handbook Meteorite Collections, U. S. N. M., p. 93. 3 Site. Akad. Wiss. Wien., 49, 1864, p. 490. 4 C. R. Acad. Sci., Paris, 66, 1868, p. 571. 5 Meleorites, (Fremy's Encyclopedie Chimique), 1884, p. 152. 7 Tschermak's Min. Pet. Mittheil, 34, 1917, p. 272 There being no available slices for comparison a portion of the Four Corners meteorite, shown in pl. 2 was sent to Dr. Meunier, from whom was received a reply of which the following is an abstract: "La photographie que vous m'aves envoyé de votre météorite metamorphique que vous comparez si vraisembleblement a la pierre de Deesa, est remarquable par sa netteté et par son eloquence; on y voit que l'alliage metallique a fait eruption an travers d'un bane de roche grisatre ordinari et la noiree jusqu'au coeur de la substance, le metal s'est consolidé tres tranquellement ce qui lui a permis de presider a la cristallization de aiguilles et de lamelles a composition chemique parfaitement definie. Votre echantillon est des plus preceux pour prouver de communnaté de gisementide different types de meteor-ites dans une masse apporté parun seul bolide conformenent a l'opinion que J'ai developpeé." Meunier, April 21, 1924. | |